1. Field of the Invention
This invention relates in general to condensing furnaces and, in particular, to the coupling box that connects the primary heat exchanger and condensing heat exchanger of a condensing furnace. More specifically, but without restriction to the particular embodiment hereinafter shown and described, this invention relates to a baffle positioned within the coupling box to direct flow of flue gas evenly throughout the coupling box.
2. Discussion of the Prior Art
The residential heating industry has benefitted with the advent of condensing gas furnaces. These furnaces typically include a primary heat exchanger positioned adjacent a secondary or condensing heat exchanger. A blower provides air flow over the heat exchangers to produce heated air that may be channeled and directed to a desired location.
Both the primary heat exchanger and the condensing heat exchanger include cells with channels formed therein to direct the flow of flue gas. These cells are positioned side by side in a parallel manner and are provided with a predetermined spacing to allow the blower air to flow around the cells. The blower air is heated by convection as it moves over the cells.
Gas is provided to the furnace by a gas manifold, and manifold orifices then direct the gas into burners contained in a burner box. The gas is ignited as it exits the burners contained in the burner box. The heated flue gas is then directed into the primary heat exchanger cells and is induced to move therethrough. The channels provided in the primary heat exchanger cells eventually terminate at discharge ports. The discharge ports of the primary heat exchanger are typically aligned and secured in a first sheet metal panel.
The condensing heat exchanger of these furnaces is configured in a similar manner. A series of condensing cells is provided in a side by side manner. Each of these condensing cells has an inlet port for receiving the flue gas discharged from the primary heat exchanger. The inlet ports of the condensing heat exchanger cells are aligned and secured in a second sheet metal panel.
The two heat exchangers are mounted together to form a single integral unit capable of receiving and heating clean intake air provided from the blower. Once mounted together in a single unit, the two sheet metal panels join to form a single planar region containing the discharge ports of the primary heat exchanger and the inlet ports of the condensing heat exchanger.
In order for the furnace to function properly, it is necessary to fluidly connect, in a closed manner, the discharge ports of the primary heat exchanger to the inlet ports of the condensing heat exchanger to prevent the flue gas from mixing with the intake air provided by the blower. This has typically been accomplished by providing a shallow pan-shaped coupling box to cover the planar region containing the discharge ports of the primary heat exchanger and the inlet ports of the condensing heat exchanger.
Proper functioning of condensing furnaces also requires that the water vapor existing in the combustion products carried in the flue gas is condensed only in the condensing heat exchanger and not elsewhere within the furnace. Condensation is prevented from forming in the primary heat exchanger by directing the proper air flow over the heat exchanger as a function of temperature. The coupling box, however, is not situated directly within the air flow and is thus subject to possible temperature variations. These temperature variations are further maintained because the heated flue gas does not evenly flow through the coupling box. Such temperature variations in prior coupling boxes can cause water vapor existing in the combustion products carried in the flue gas to condense within the coupling box. When water thus condenses in the coupling box, the box becomes subject to corrosion and ultimate failure resulting in possible leakage of flue gas into the immediate environment.